Systematic characterization of excited states in π-conjugated polymers

Exact finite chain calculations within a diagrammatic exciton basis give pictorial descriptions of all excited states of π-conjugated polymers. In linear chain polymers the 1Bu is an exciton, and the fundamental two-photon states can be broadly classified into triplet–triplet, charge-transfer and singlet–singlet excitations. The mAg, a two-photon state that plays a strong role in nonlinear optics, is a correlated charge-transfer state. The singlet–singlet states occur higher in energy and split into bound biexcitons and a continuum of free two-exciton states.